1. Field of the Invention
The present invention relates to a printing apparatus and a print controlling method, and particularly, to a conveying control of a printing medium before and after timing when the print medium leaves from a conveying roller at the upstream side of a printing region in print-medium conveying.
2. Description of the Related Art
Conveyance of a print medium such as a print paper in a printing apparatus such as an ink jet printer is generally carried out by a conveying mechanism formed of a conveying roller and a pinch roller provided at the upstream side of a printing region in a conveying path and by a conveying mechanism formed of a paper discharging roller and a spur provided at the downstream side thereof. In regard to the print medium conveyance by these mechanisms, for example, when performing a so-called margin-less printing, the conveyance of the print medium may be carried out in a state where the conveying mechanism at the upstream side or at the downstream side is not involved in the conveyance. More specifically, at the time of performing the printing until a rear end of the print medium by ejecting ink even on a portion out of the rear end of the print medium, the print medium is conveyed in a state of sandwiching the print medium only by the paper discharging roller and the spur at the downstream side.
It is conventionally known that, while a conveyance state transfers to the conveyance state in which the print medium is sandwiched only by the paper discharging roller and the spur at the downstream side, the print medium may be conveyed by an unexpected amount when the print medium disengages from a state of being held between the conveying roller and the pinch roller at the upstream side. This event is a phenomenon called a so-called kicking-away, and particularly since a conveying amount of the print medium can not be definitely controlled, this phenomenon causes the difficulty of controlling the conveying amount around a point on the conveying path of the print medium at which the print medium disengages from the state of being held between the conveying roller and the pinch roller at the upstream side.
For overcoming this problem, Japanese Patent Laid-Open No. 2008-050083 discloses a conveying control in which a certain range of the conveying path around a point at which the rear end of the print medium passes (engages from) the conveying roller at the upstream side is defined as a range where the rear end of the print medium can not be stably stopped in a desired position. In addition, this conveying control is designed to exclude the conveyance of a conveying amount by which the rear end of the print medium is positioned to stop within this range.
FIG. 1 is a diagram explaining the conveying control described in Japanese Patent Laid-Open No. 2008-050083 and shows a conveying operation around the point at which the print medium passes the conveying roller. In the figure, reference sign N denote a position of a nip formed of a conveying roller 20 and a pinch roller 40 in a conveying direction. A region of A to B, which contains the nip position N and is a range around the nip position N, is a stop-unstable region in which the rear end of the print medium described above can not be stably stopped in a desired position. A paper 500 as the print medium is conveyed in an arrow E direction in the figure in response to rotation of the conveying roller, while the print paper 500 is held between the conveying roller 20 and the pinch roller 40. A printing head 501 is provided with a plurality of nozzles (not shown) as printing elements, which are arranged in the same direction as the conveying direction of the paper.
Black circles in the figure show positions to which the rear end of the paper 500 moves by each paper conveyance carried out for each scanning by the printing head 501. Reference signs F1, Fv, F2 and F3 each show a conveying amount of the paper conveyance for each scanning by the printing head 501. It should be noted that in the following explanation, these signs F1, Fv, F2 and F3 may be also used to denote a conveying operation of each conveying amount.
As shown in FIG. 1, the conveying control is performed in such a manner that the rear end of the paper 500 is positioned and stopped to avoid the stop-unstable region (between A and B). Specifically, a conveying operation of a predetermined conveying amount F1, in which the paper 500 is relatively stably conveyed in a state of being held between a pair of the conveying roller and the pinch roller at the upstream side and between a pair of the paper discharging roller and the spur at the downstream side, is performed several times. Thereafter, before transferring the conveyance from the conveying amount F1 to a conveying amount F2 smaller than the conveying amount F1, the conveyance of a conveying amount Fv is carried out. The conveyance of the conveying amount F2 is provided with a small conveying amount that is previously determined in consideration of a decrease in conveyance accuracy upon performing printing on the vicinity of the rear end of the paper, and the number of the nozzles used in the printing head 501 is reduced in response to the small conveying amount.
A distance from a position after the paper 500 is conveyed by the conveyance F1 to a position A which is an end of the stop-unstable region where the stop position of the end of the paper is unstably determined is detected, and the conveying amount Fv is defined based upon this distance. More specifically, the conveying amount Fv is defined in such a manner that the rear end of the paper 500 reaches the position A when the conveyance F2 is carried out four times after the conveyance Fv. Therefore, by carrying out the conveyance of a conveying amount F3 (=AB+α) after the paper is conveyed to a point where the rear end of the paper is positioned at the position A, the rear end of the paper can stop in the stop-stable region at the downstream side from B point through the region A to B.
FIG. 2 is a diagram showing the paper conveyance shown in FIG. 1 by a change in positional relation between the printing head and the paper. In FIG. 2, for simplification of the drawing, positions of the printing head 501 relative to the paper at the time of conveying the paper 500 in the arrow E direction are shown in such a manner that the printing head 501 moves. The relatively moved printing head 501 is denoted by different numerals 502 to 510 in accordance with a position thereof. FIG. 2 shows an example of a so-called four-pass printing where the printing in a given area in accordance with a conveying amount of the paper 500 is completed by four times of scans. For the four-pass printing, a plurality of nozzles in the printing head 501 (502 to 510) are basically divided into four groups for use. In this figure, four divided nozzle groups in the printing head 501 are respectively denoted by signs 501a, 501b, 501c, and 501d (the same is applied to the printing heads 502 to 510 in the other positions). Here, an arrangement length of each of the four divided nozzle groups (number of nozzles×nozzle pitch) is set to be equal to the conveying amount F1 described above. That is, an entire arrangement length of the nozzles in the printing head is F1×4.
In a case of performing the conveying control described in Japanese Patent Laid-Open No. 2008-050083, a reduction of a throughput may occur due to how to define the conveying amount Fv. More specifically, in Japanese Patent Laid-Open No. 2008-050083, the conveying amount Fv is defined based upon each conveying amount F2 of four times of conveyances to be carried out after the conveyance by the conveying amount Fv. Specifically the conveying amount Fv is defined by adding a remainder, which is obtained by dividing the distance to the above position A by the conveying amount F2, to the conveying amount F2. Therefore, as an example shown in FIG. 2, the conveying amount Fv may be larger than the conveying amount F1 in a usual region depending on a magnitude of the conveying amount F2. In a case where the conveying amount Fv is thus larger than the conveying amount F1, when the conveying amount F1 is set to the amount found by dividing the nozzle arrangement length of the printing head by the number of passes (four in the above example) without its modification, an area where the printing is not completed is to be produced. More specifically, as shown in FIG. 2, there is to be produced an area g in the paper 500, although the printing in the entire area is originally designed to be completed by the nozzle groups 502a, 503b, 504c, and 505d, which can not become complementary by the nozzle group 505d. Accordingly, the conveying amount is required to be small in the conveyance of the conveying amount F1 in the usual region, and also the number of the nozzles for use in the nozzle group is restricted in response to the reduction of the conveying amount. As a result, conveyance F1 in the usual region where the number of times of the conveyances is the largest is carried out in an amount smaller than the maximum-possible conveying amount, thus reducing the throughput largely.